Chapter 3
Features, advantages and applicability of CCTs
(Coal-Based Power Generating Technologies)
3.1. Coal-fired power plants
Fig.3.1.1 shows a schematic overview of a typical and current coal fired power plant
constructed in Japan. Low NOx burner, De-NOx, De-SOx and Electrostatic Precipitator (ESP) are
essential. Gas-gas heater (GGH) is equipped to avoid white smoke from the stack by the
warming-up of the flue gas exhausted from wet type De-sulfurization equipment. Ancillary
equipment are introduced in chapter 4.
Reheat steam
Main steam
Figure 3.1.1 Schematic overview of a typical coal fired power plant installed in Japan
Source: Japan Coal Energy Center
3.2 History of steam conditions for coal-fired power plants
(1) Improvement of steam condition
Development history of steam conditions for power plant in Japan is shown in Figure 3.2.1.
The steam pressure and temperature have been intended to increase for the improvement of
power generation efficiency. Supercritical power plant started in 1967 with oil and gas fired
boiler (Steam pressure in 24.1MPa, main steam temperature in 538 degrees C and re-heater
steam temperature in 566 degrees).
Coal fired supercritical power boiler started in 1983 with
24.1 MPa and 538 degrees C steam (both superheated and reheated steam). Ultra supercritical
power unit started in 1993 at 24.1 MPa and 538 degrees C of main steam and 593 degrees C of
re-heater steam. As of 2014, the latest coal fired power plant designed at 25MPa and 600 degrees
C main steam and 620 degrees C reheated steam started in2009.
Figure 3.2.1 Development of steam temperature and pressure.
Source: Japan Coal Energy Center
(2) Comparison of Subcritical unit and supercritical unit
Table 3.2.1 shows the main comparative features of boiler designed by new technology to
old one.
type
Table 3. 2. 1 Comparison of new designed boiler to old one.
Subcritical unit
Supercritical and Ultra-supercritical units
(Drum type boiler)
(Once-through type boiler)
To
Turbine
Super-heater
Water circulation
Riser pipes
Furnace Wall tube
(Water-cooled)
To
Turbine
Economizer
ρ2
Feed-water
ρ1
Down-comers
Densityρ1>ρ2
Burners
Features
Drum
Super-heater
Boiler water circulation
Furnace Wall tube
(Water-cooled)
Furnace Wall tube
(Water-cooled)
Burners
Economizer
Feed-water
・Boiler-water is fed to drum through the economizer.
・ Fluid (feed-water) at supercritical pressure experiences a
・Boiler-water is supplied to furnace wall through down-comer and heated up
continuous transition from water-like to steam-like
in the furnace. Heat addition generates a steam-water mixture and returns to
characteristics. The fluid passed through the economizer in
drum. In the drum, the steam is separated from boiler water and supplied to
liquid phase flows to the furnace wall tubes and is heated-up in
super-heater. Superheated steam is supplied to turbine for power generation.
the furnace and changed to vapor (steam) phase and connected
・In circulation, gravity acting on the density difference between the sub-cooled
to super-heater. Superheated steam is supplied to turbine for
water in the down-comer and steam water mixture in the heating tube circuit
power generation.
produces the driving force for circulation.
・No two phases state occurs in the furnace and drum is not
・Maximum capacity of the plant is limited up to about 600MW due to the
required.
limitation of the drum sizing.
Steam Conditions
Subcritical
Supercritical
Ultra-supercritical
16.6
24.1
24.1
538 - 566
538 - 566
593 - 620
Drum
Once-through
Once-through
Generating Efficiency
low
high
highest
Fuel/ Exhaust gas
more
less
Least *1
Water quality control
easy
severe*2
more severe *2
Steam temperature control
easy
severe
Load changing rate
low
high
Start-stop time
long
quick
Pressure MPa (Typical)
Temperature ℃ (Typical)
Boiler type
Operation
relatively easy (base)
Quick responding action required *3
Maintenance
relatively easy (base)
Establishment of maintenance procedure is required *4
Main tube material
low alloy
Low/ high alloy
Ferritic stainless *5
Remarks
*1. Less exhaust gas contributes to less amount of NOx, SOx, Particulate matter and CO 2 emission.
*2. Impurities are entrained to turbine or accumulated in boiler tubes.
*3. Rapid steam pressure and temperature control is required due to less holding amount of boiler water.
*4. Considering characteristics of new materials for high temperature use, maintenance procedure is required to republish.
*5. Austenitic stainless steel tubes is used for high temperature steam condition.
*6. Typical side view of Subcritical Boiler
*7. Typical side view of Supercritical Boiler
Source: Japan Coal Energy Center
Figure 3.2.2 Typical side view of Subcritical Boiler*6
Source: The Institute of Electrical Engineers of Japan
Pendant Super-heater
Pendant Re-heater
Horizontal Re-heater
Horizontal
Super-heater
Evaporator
Economizer
Coal
Banker
DeNOx
Burner
Air-heater
Pulverizer
Figure 3.2.3 Typical side view of Supercritical Boiler*7
Source: The Institute of Electrical Engineers of Japan
3.3 Ultra-supercritical coal-fired power plants
In the 90th, National project was started to develop 600 degrees C class coal fired power plants to
improve the thermal efficiency. First USC (≥24.1 MPa and 593 ℃) in Japan was built in 1993
whose capacity was 700MW.
Since then the steam conditions in USC for all coal fired power plants have been adopted in
Japanese power station. Furthermore the development for the application of higher steam
temperature has been proceeded and as of 2014, the highest super-heater and re-heater steam
temperatures are in 600 ℃ and 620 ℃ respectively.
. All of them have been operating with a high efficiency and high availability.
Fig.3.3.1 shows power generation efficiency and CO2 reduction rates for various steam
conditions of SC/USC units. Efficiency improve from 538 degree C class to 625 degree C is
relatively +5% and CO2 reduction is -4.5%. Fig.3.3.2 is a view of Isogo Power Station.
Figure 3.3.1 Efficiency and CO2 reduction rate
Source: Japan Coal Energy Center
Figure 3.3.2 Up-to-date USC, Isogo No.1 and No.2 Units
(600MW respectively, From J-POWER Homepage)
Fig 3.3.3 Boiler side view of Ultra-supercritical unit
(Isogo Unit No.1; 600MW)
For the next step, the study for a 700 degree C class USC power plant started in 1998. It is called
as A-USC (Advanced USC) whose targeted net efficiency is around 50% (LHV basis).
3.4 Integrated Coal Gasification Combined Cycle (IGCC)
(1) General
Coal fired power plants play an important role in providing energy at low prices
because coal is abundant, efficient and less expensive than most other energy options
and will remain an important part of energy future in the world. However coal fired
power plants emit considerable quantity of carbon dioxide (CO 2 ), a greenhouse gas
(GHG), into atmosphere compared to other power generation plants and required to be
improved in environmental performance.
IGCC has been developed to improve the power generation efficiency using gasifier
technology to turn coal into synthesis gas (syngas) for gas turbine power generation.
The plant is called integrated because the syngas produced in the gasification section is
used as fuel for the gas turbine in the combined cycle and steam produced by syngas
cooler in the gasification section and heat recovery steam generator (HRSG) installed
gas turbine exhaust section is used by steam turbine in combined cycle. Figure 3.4-1
shows outline of IGCC.
Figure3.4.1 Outline of IGCC
Source: Joban Joint Power., Ltd.
Figure3.4.2 shows thermal efficiency of typical power generation plant.
Figure3.4.2 Thermal efficiency of typical power generation plant
Source: Japan Coal Energy Center
(2) Demonstration Plant
Figure3.4-3 shows 250MW demonstration plant installed at Nakoso power station of Joban Joint
Power Co., in Japan supplied by Mitsubishi Heavy Industries, Ltd..
The plant had successfully completed its demonstration operation under Clean Coal Power R&D
Co., Ltd. and has started its commercial operation since April of 2013 under Joban Joint Power Co.,
the new owner of 250MW Nakoso IGCC plant.
Gasifier
HRSG
GT / ST
Gas
Clean-Up
Figure 3.4.3 250 MW IGCC Demonstration Plant
Source: Joban Joint Power., Ltd.
(3) Beneficial features
IGCC system has following features compared with conventional coal fired power generation
systems.
1) High plant efficiency
2) Low pollution in NOx, SOx, CO2 and dust emission
3) Reduction of ash volume and protection from heavy-metals elution after landfill by melting
of ash in gasifier and exhausted as vitric slag.
4) Coal with low ash melting temperature, ill-suited for pulverized coal fired boiler, can be
used.
3.5 Japan’s Typical Coal-Fired Power Plants
(1) Tokyo Electric Power Co., Inc.
1) Hirono Coal-fired Power Plant (Space: 1,320,000M2) 1
a) Unit Specification
No.
Nominal
Output(MW)
Steam condition
Temp.
COD
Pressure
#5
600
600/600℃
24.5MPa
June/2004
#6
600
600/600℃
24.5MPa
Dec./2014
Unit1,2,3,4 are oil-fired Units.
b) Overview of TPS
1
Reference: Tokyo Electric Power HP
http://www.tepco.co.jp/cc/press/betu13_j/images/131203j0101.pdf , Jcoal Coal
Data Bank
c) Layout of TPS
2) Hitachinaka Coal-fired Power Plant (Space:1,410,000M2) 2
a) Unit Specification
No.
Nominal
Steam condition
COD
Output(MW)
Temp.
Pressure
#1
1000
600/600℃
24.5MPa
June/2003
#2
1000
600/600℃
24.5MPa
Dec./2013
b) Overview of TPS
Reference: Tokyo Electric Power HP
http://www.tepco.co.jp/cc/press/betu13_j/images/131218j0101.pdf,Jcoal ,Coal Data
Bank
2
c) Layout of TPS
(2) CHUBU Electric Power Co., Inc.
Hekinan Coal - Fired Power Plant (Space: 1,600,000M2) 3
a) Unit Specification
No.
3
Nominal
Steam condition
COD
Output(MW)
Temp.
Pressure
#1
700
538/566℃
24.1 MPa
Oct./1991
#2
700
538/566℃
24.1 MPa
June/1992
#3
700
538/593℃
24.1 MPa
Apr./1993
#4
1000
566/593℃
24.1 MPa
Nov./2001
#5
1000
566/593℃
24.1 MPa
Nov./2002
Reference: Material was supplied by CHUBU Electric Power Co.,Inc.
b) Overview of TPS
c) Layout of TPS
(3) Electric Power Development Co., Ltd
Isogo Coal-fired Power Plant (Space: 120,000M2) 4
a) Unit Specification
No.
Nominal
Steam condition
COD
Output(MW)
Temp.
Pressure
#1
600
600/610℃
25MPa
Apr./2002
#2
600
600/620℃
25MPa
July/2009
b) Unit Specification
No.
Nominal
Steam condition
Output(MW)
Temp.
Pressure
#1
600
600/610℃
25MPa
Apr./2002
#2
600
600/620℃
25MPa
July/2009
c) Overview
4
COD
of TPS
Reference: Guidebook of Isogo Thermal Power Station Published by Electric Power Development
Co.,Ltd
d) Layout of TPS